The formula
Days sales outstanding answers one question: how many days, on average, do customers take to pay. Divide accounts receivable by total credit sales, then multiply by the days in the period. A DSO of 30.00 days means customers take a month, on average, to pay.
Step 1 — Find the accounts receivable
Start with the accounts receivable: the money customers still owe for goods or services already delivered, from the balance sheet. It is the unpaid invoices at the end of the period. Use the same period for everything. On the worked example the accounts receivable is $180,000.00.
Step 2 — Find the credit sales
Now find the total credit sales in the period, from the income statement. Only CREDIT sales count — cash sales are excluded, because cash is already collected. Including cash sales would shrink the DSO and flatter the result. On the worked example the total credit sales are $2,190,000.00.
Step 3 — Divide the accounts receivable by the credit sales
Divide the accounts receivable by the total credit sales: the share of the period’s credit sales still sitting unpaid. On the worked example it is $180,000.00 ÷ $2,190,000.00 = 0.082192.
Step 4 — Multiply by the days in the period
Multiply that share by the days in the period, usually 365 for a year or 90 for a quarter. On the worked example it is 0.082192 × 365 = 30.00 days.
Step 5 — Work out the accounts receivable the target needs
Multiply total credit sales by the target DSO and divide by the days in the period. For a 25-day target, the accounts receivable needed is $2,190,000.00 × 25 ÷ 365 = $150,000.00. To reach a 40-day DSO on the same sales, the smallest whole-dollar accounts receivable is $240,000 — at $239,999 the receivables are $1 short of the $240,000 needed, and the unrounded DSO is 39.999833 days, which displays as 40.00 days after rounding.
Step 6 — Work out the credit sales the target needs
Multiply the accounts receivable by the days in the period and divide by the target DSO. For a 25-day target, the credit sales needed are $180,000.00 × 365 ÷ 25 = $2,628,000.00. The smallest whole-dollar credit sales for the DSO to stay at or below 20 days is $3,285,000 — at $3,284,999 the sales are $1 short of the $3,285,000 needed.
Step 7 — Check the result against the 30-day strong line and the 60-day slow line
Under 30 days is generally strong, 30 to 45 days is typical for many businesses, and over 60 days usually means collections are slow and cash is tied up in unpaid invoices. On the worked example the DSO is 30.00 days, so the business sits right on the strong line. The largest whole-dollar accounts receivable for the DSO to stay at or below 15 days is $90,000, and to stay at or below 45 days it is $270,000.
Three worked examples
The headline example: $180,000.00 of accounts receivable and $2,190,000.00 of credit sales over 365 days. The DSO is $180,000.00 ÷ $2,190,000.00 × 365 = 30.00 days, the receivables needed for the 25-day target are $150,000.00, and the sales needed are $2,628,000.00. With $90,000.00 of receivables instead, the DSO is 15.00 days; with $1,095,000.00 of sales, 60.00 days; with $270,000.00 of receivables, 45.00 days; over a 90-day period, 7.40 days; with $45,000.00 of receivables, 7.50 days; with $3,650,000.00 of sales, 18.00 days; with $0.00 of receivables, 0.00 days — nothing outstanding. Use the days sales outstanding calculator for your own numbers.
Two reverses to check your answer
The largest whole-dollar accounts receivable for the DSO to stay at or below 30 days is $180,000 — at $180,000 the DSO is 30.00 days; at $180,001 the receivables are $1 over the $180,000 allowed, with an unrounded DSO of 30.000167 days, which displays as 30.00 days after rounding. The smallest whole-dollar credit sales for the DSO to stay at or below 25 days is $2,628,000 — at $2,628,000 the DSO is 25.00 days; at $2,627,999 the sales are $1 short of the $2,628,000 needed, with an unrounded DSO of 25.000010 days, which displays as 25.00 days after rounding.
What average accounts receivable is, and why it is an average
Average accounts receivable is (opening accounts receivable + closing accounts receivable) ÷ 2: the receivables at the start plus the receivables at the end, divided by two. A single end-of-period snapshot misleads: a business that bills heavily in December and collects in January would show huge receivables in December and small ones in February, and neither snapshot is the year. The average is steadier, because receivables swing through the year. A business with monthly figures can average all twelve months instead.
What a high DSO means — and what a low DSO means
A high DSO means more sales on credit but slower cash: the goods are sold and the business is still waiting to be paid, so cash is tied up in unpaid invoices. A low DSO means cash comes in fast, but it can also mean credit terms are too strict and scare off customers. Retail businesses often run near 20 days because customers pay fast; manufacturers often run 40 to 50 days; construction and professional services can run 60 days or more, because invoices are large and payment terms are long. DSO is the mirror of accounts receivable turnover: DSO = 365 ÷ accounts receivable turnover.
What to do when the DSO is high
A DSO over 60 days means each dollar of credit sales takes more than two months to arrive. Collect more by invoicing on delivery day, shortening payment terms, offering a small early-payment discount, and chasing overdue invoices the week they fall due. And check new customers’ credit before offering terms, so the extra sales are sales that actually get paid. The accounts receivable needed for a 25-day DSO is $150,000.00 — every dollar collected below that line pulls the DSO down.
How days sales outstanding differs from inventory turnover, gross profit margin and days payable outstanding
Inventory turnover divides cost of goods sold by average inventory: it tests how fast STOCK sells, not how fast customers pay. Gross profit margin divides gross profit by revenue: it tests what share of each sales dollar remains after the direct cost of goods sold, not the speed of collection. Days payable outstanding is the mirror image: it tests how fast YOU pay suppliers, while DSO tests how fast customers pay you. The cash conversion cycle combines all three into the full time from paying for stock to collecting the cash. DSO is the receivables test; inventory turnover is the stock test; gross profit margin is the profit test. See the inventory turnover calculator and the guide to calculating inventory turnover, and the gross profit margin calculator.